1. Technical field
The present invention relates to an ammoxidation catalyst composition, and a process for producing acrylonitrile or methacrylonitrile using the same. More particularly, the present invention is concerned with an ammoxidation catalyst composition for use in the process for producing acrylonitrile or methacrylonitrile by reacting propylene with, or reacting isobutene or tert-butanol with a molecular oxygen-containing gas and ammonia, the ammoxidation catalyst composition comprising an oxide catalyst composition comprised of molybdenum, bismuth, at least one rare earth element, iron, nickel, at least one element selected from magnesium and zinc, and at least one element selected from potassium, rubidium and cesium, wherein the atomic ratio of the sum of bismuth and the at least one rare earth element, relative to twelve atoms of molybdenum, is from 0.5 to 2 and the atomic ratio of the at least one rare earth element to the sum of bismuth and the at least one rare earth element is from 0.6 to 0.8. By use of such an ammoxidation catalyst composition, not only can acrylonitrile or methacrylonitrile be produced in high yield, but also a lowering of the yield of acrylonitrile or methacrylonitrile can be effectively suppressed even after the operation of the production process has been conducted for a prolonged period of time. The present invention is also concerned with a process for producing acrylonitrile or methacrylonitrile using such an ammoxidation catalyst composition.
2. Prior Art
It has been well known to produce acrylonitrile or methacrylonitrile by ammoxidation of propylene, or of isobutene or tert-butanol, namely, a reaction of propylene with, or of isobutene or tert-butanol with a molecular oxygen-containing gas and ammonia. A number of proposals have been made with respect to catalysts for use in the ammoxidation of propylene, or of isobutene or tert-butanol. For example, U.S. Pat. No. 3,226,422 proposes an oxide catalyst containing molybdenum, bismuth and iron, and Examined Japanese Patent Application Publication No. 38-19111 proposes an oxide catalyst containing antimony and iron. Further, various improvements have been proposed with respect to these ammoxidation catalyst systems.
For example, each of British Patent No. 1,445,512 and U.S. Pat. No. 4,746,753 discloses a catalyst containing an alkali metal and thallium in addition to molybdenum, bismuth and cerium. Examined Japanese Patent Application Publication No. 61-43094 discloses a catalyst comprising molybdenum, tungsten, bismuth and cerium. U.S. Pat. No. 4,969,390 discloses an oxide catalyst containing at least one element selected from iron, chromium, aluminum and bismuth, in addition to molybdenum, tellurium and cerium. U.S. Pat. No. 4,192,776 discloses an oxide catalyst containing, in addition to molybdenum, bismuth and iron, at least one element selected from nickel and cobalt, and at least one element selected from an alkali metal, a rare earth element, tantalum and niobium. U.S. Pat. No. 4,443,556 discloses an oxide catalyst containing molybdenum, bismuth and iron as essential elements, and also containing at least one element selected from cerium, lanthanum, neodymium, praseodymium, samarium, europium and gadolinium, and at least one element selected from potassium, rubidium and cesium. Unexamined Japanese Patent Application Laid-Open Specification No. 59-204163 discloses a catalyst containing, in addition to molybdenum, bismuth, phosphorus and silicon, at least two elements selected from iron, cobalt, nickel, copper, zirconium and potassium, and at least one element selected from manganese, cerium, thorium, yttrium, lanthanum and thallium. However, in the above prior art documents, there are no working examples using a catalyst composition satisfying the specific requirements of the catalyst composition of the present invention.
Further, each of U.S. Pat. No. 5,093,299, U.S. Pat. No. 5,175,334 and U.S. Pat. No. 5,212,137 discloses a catalyst containing molybdenum, bismuth, iron, nickel, magnesium, potassium and cesium as essential elements and optionally containing cobalt, manganese, chromium, phosphorus, antimony, tellurium, sodium, cerium and/or tungsten, and a process for producing acrylonitrile or methacrylonitrile using such a catalyst. However, it is noted that in the working examples of the above three U.S. patent documents, a catalyst containing cerium is not used. It is needless to say that, in these patent documents, neither working example nor description is found with respect to use of any other rare earth element.
The catalysts disclosed in the above-mentioned patent documents are greatly improved in respect of the yield of acrylonitrile or methacrylonitrile at the initial stage of reaction. However, those catalysts are still unsatisfactory in respect of the yield of acrylonitrile or methacrylonitrile when the operation of the production process is conducted for a prolonged period of time.